The invention relates to new and useful improvements in a weight sensor. The weight sensor, which operates according to the principle of electromagnetic force compensation, and the essential parts of which are produced from a single block of material, has a vertically movable load receiver. The load receiver is guided in parallel guide elements, which are articulated to a fixed base body of the block of material. The load receiver is effectively coupled to several force-translating elements which are serially arranged between the load receiver, a coil carrier, and the base body.
Weight sensors of this type are known, for example, from European Patent Application EP 518 202 A1. A drawback of this known construction is that there is no space left within the one-piece block for the permanent magnet. In European Patent Application EP 518 202 A1, the permanent magnet is therefore mounted outside of the one-piece block and the last translation lever of several translation levers is extended by lateral extension pieces which bear the coil. However, as a result, the functional and price advantages of the single-piece construction are partially lost. In addition, the arrangement of all three translation levers one above the other requires a large overall height. All parallel guide elements and force translating elements are dimensioned in accordance with the width of the block and sequentially arranged one above and behind the other. As a result, the structural shape is relatively high and narrow.
A similar weight sensor with two translation levers is known from German Patent Application DE 195 40 782 A1. It is difficult, however, to obtain a large force translation ratio with two translation levers, such as is required for particularly high-load scales having a maximum load of 30 to 150 kg. Also, in the design of German Patent Application DE 195 40 782 A1, there is no room available for the installation of a third translation lever. In particular, it is problematical to fix the third translation lever to the housing.
Due to its monolithic construction, the weight sensor according to German Patent Application DE 195 40 782 C1 has very good measuring properties and an outstanding long-term stability. Because of its two translation levers with their combined high translation ratio, this weight sensor is particularly suited for heavy loads above 10 kg.
The only drawback of this weight sensor is that its sensitivity can be checked and, if necessary, adjusted only through external application of calibrating weights. However, the handling of external calibrating weights xe2x89xa710 kg is complicated and cumbersome.
It is therefore already known (for example from U.S. Pat. No. 2,832,535 and U.S. Pat. No. 4,932,487) to use internal calibrating weights in weight sensors composed of individual pieces, which calibrating weights are not applied directly to the load receiver but rather to one of the translating levers. As a result, the calibrating weight can remain much smaller than the maximum load of the balance and yet has the effect of a calibrating weight at maximum load due to the translating ratio. Applying this principle to a monolithic weight sensor of the type described above, however, is difficult since, as a result of the monolithic construction, space in the weight sensor is very restricted.
In a partially monolithic weight sensor, in which all but the last translating lever, all coupling elements, and the guides are fabricated from one block by means of thin cuts, it is further known from German Patent Application DE 196 05 087 C2 (corresponding to U.S. Pat. No. 5,866,854) to provide a coupling area for an internal calibrating weight, wherein the coupling area is parallel-guided by two additional guides. Two cross beams are attached to this coupling area as a support means for the calibrating weight. This additional parallel guide system, however, increases the overall height of the weight sensor and increases the number of spring joints by four additional joints. As a result, the spring constant of the weight sensor, and thus the likelihood of uncontrolled measured value changes, rises. Furthermore, as a result of the fastening of the cross beams to the monolithic part, material stresses are generated in this part and, therefore, the advantages of monolithic construction are again partially defeated.
Therefore, it is one object of the invention to further develop a compact construction for a weight sensor of the type mentioned above, in which all force translating elements are fabricated entirely from the block of material. It is a further object to provide a construction that does not require the initial height of the material block and the overall height of the finished weighing system to be large. The structural shape should also be suitable for coupling a calibration means in a simple manner to the force translating elements, if desired.
According to one formulation of the invention, the above and other objects are achieved by a weight sensor which includes a base body, a load receiver and a plurality of force transmission elements which are arranged between the base body and the load receiver. Furthermore, at least one of the plurality of force transmission elements is divided to form partial force transmission elements. These partial force transmission elements are symmetrically spaced from a central, vertical plane which passes through the load receiver. Moreover, at least one of the plurality of force transmission elements is arranged symmetrical in the central, vertical plane. The base body includes at least one projection that has bearing points to bear at least one of the plurality of force transmission elements.
In accordance with its broad and narrower formulations, the invention makes use of, with respect to force, symmetrical division or splitting of individual force translating elements. The projection of a base body advantageously projects relatively far in the direction of the load receiver. It is possible to use the projection""s vertical and horizontal graduations or horizontal indentations as supports or receiving bearings for several force translating elements. As a result of this spatial division according to the invention and as a result of the three-dimensional subdivision of the translating elements, a geometry is created which facilitates a compact, low monolithic construction and, in particular, allows for fabrication by milling. This configuration also allows for optional coupling or at least partial integration of calibrating means into the monolithic block with all of the advantages regarding the physical behavior of the complex measuring unit.
More particularly, the above and other objects are achieved in that at least one translating lever is divided at least partially into two partial levers. Furthermore, at least one coupling element is divided into two partial coupling elements and the partial levers and the partial coupling elements are symmetrically arranged on both sides of the projecting portion of the part that is fixed to the housing. All translating levers, all partial levers, all coupling elements, and all partial coupling elements are monolithic components of the block.
As a result of the division into partial levers and partial coupling elements, the partial levers and the partial coupling elements can be symmetrically arranged on both sides next to the centrally arranged, projecting portion of the part which is fixed to the housing. Thus, they can be fabricated from the block. In spite of this, a sufficiently stable projecting portion of the part which is fixed to the housing is maintained. Due to the symmetrical arrangement of the partial levers and the partial coupling elements, the symmetry of the force flux pattern is maintained so that the comer load sensitivity remains low. This spatial division according to the invention additionally allows one of the force translating elements to also serve as a direct support for a calibrating weight. Thereby, the calibrating weight can be disposed either inside or outside of the contour of the monolithic material block.
According to a first exemplary embodiment of the invention, a lever directly supporting a calibrating weight is a monolithic component of the material block. In a second embodiment, one of the translating levers has an additional lever arm to support the calibrating weight. This additional lever arm is a monolithic component of the material block as well.